1. Field of the Invention
The present invention relates to a system for electronically controlling one or more petroleum production wells, and more particularly, to a system for controlling wells in order to optimize the production efficiency of formation fluids.
2. History of the Prior Art
Each underground hydrocarbon producing formation, known as a reservoir, has its own characteristics with respect to permeability, porosity, pressure, temperature, hydrocarbon density and relative mixture of gas, oil and water within the formation. In addition, various subterranean formations comprising a reservoir are interconnected with one another in an individual and distinct fashion so that the production of hydrocarbon fluids at a certain rate from one area of one formation will affect the pressures and flows from a different area of an adjacent formation.
Certain general characteristics are, however, common to most oil and gas wells. For example, during the life of any producing well, the natural reservoir pressure decreases as gases and liquids are removed from the formation. As the natural downhole pressure of a gas well decreases, the well bore tends to fill up with liquids, such as oil and water, which block the flow of the formation gas into the borehole and reduce the output production of the well. In such gas wells, it is conventional to periodically remove the accummulated liquids by artificial lift techniques which include plunger lift devices, gas lift devices and downhole pumps. In the case of oil wells within which the natural pressure has decreased to the point that oil does not spontaneously flow to the surface, fluid production is maintained by artificial lift methods such as downhole pumps and by gas injection lift techniques. In addition, certain wells are frequently stimulated into increased production by secondary recovery techniques such as the injection of water and/or gas into the formation to maintain reservoir pressure and to cause a flow of fluids from the formation into the wellbore.
In oil and gas wells wherein the ambient reservoir pressure has been substantially depleted, two general techniques are commonly used: (1) plunger lift and (2) gas lift.
Plunger lift production systems include the use of a small cylindrical plunger which travels through tubing extending from a location adjacent the producing formation down in the borehole to surface equipment located at the open end of the borehole. In general, fluids which collect in the borehole and inhibit the flow of fluids out of the formation and into the wellbore, are collected in the tubing. Periodically the end of the tubing is opened at the surface and the accumulated reservoir pressure is sufficient to force the plunger up the tubing. The plunger carries with it to the surface a load of accummulated fluids which are ejected out the top of the well thereby allowing gas to flow more freely from the formation into the wellbore and be delivered to a distribution system at the surface. After the flow of gas has again become restricted due to the further accummulation of fluids downhole, a valve in the tubing at the surface of the well is closed so that the plunger then falls back down the tubing and is ready to lift another load of fluids to the surface upon the reopening of the valve.
A gas lift production system includes a valve system for controlling the injection of pressurized gas from a source external to the well, such as another gas well or a compressor, into the borehole. The increased pressure from the injected gas forces accumulated formation fluids up a central tubing extending along the borehole to remove the fluids and restore the free flow of gas and/or oil from the formation into the well. In wells where liquid fall back is a problem during gas lift, plunger lift may be combined with gas lift to improve efficiency. Such a system is shown in U.S. Pat. No. 4,211,279 issued Jul. 8, 1980 to Kenneth M. Isaaks.
In either case, there is a requirement for the periodic operation of a motor valve at the surface of the wellhead to control either the flow of fluids from the well or the flow of injection gas into the well to assist in the production of gas and liquids from the well. These motor valves are conventionally controlled by timing mechanisms and are programmed in accordance with principles of reservoir engineering which determined the length of time that a well should be either "shut in" and restricted from flowing gas or liquids to the surface and the time the well should be "opened" to freely produce. Generally, the criteria used for operation of the motor valve is strictly one of the elapse of a pre-selected time period. In most cases, measured well parameters, such as pressure, temperature, etc. are used only to override the timing cycle in special conditions.
For example, U.S. Pat. No. 4,354,524 discloses a pneumatic timing system which improves the efficiency of using injected gas to artifically lift liquids to a well surface by means of the plunger lift technique. U.S. Pat. No. 3,336,945 to Bostock et al discloses a pneumatic timing device for timing the intermittent operation and/or injection of wells to increase the production. U.S. Pat. No. 4,355,365 to McCracken et al discloses a system for electronically intermitting the operation of a well in accordance with prior art timing techniques wherein the well is allowed to flow for a first pre-selected period and then shut in for a second pre-selected period to increase the production from the well. The differential control system manufactured by Plunger Lift System, Inc. of Marietta, Ohio serves to operate a plunger lift completion in accordance with a gating system in which measured values of pressure and fluid levels are compared with pre-set values. U.S. Pat. No. 4,150,721 to Norwood discloses a similar gas well controller system which also utilizes digital logic circuitry gating to operate a well in response to a timing counter and certain measured well parameters.
Under certain circumstances, however, the mere timed intermittent operation of a single motor valve to control either outflow from the well or gas injection to the well will not effect maximum production nor will operation based upon a mechanical comparison of well parameters with preset maximum and minimum values. It is inefficient and costly to inject gas into a wellbore which does not contain liquids which require artificial lift or when the well is flowing naturally with a satisfactory production rate. Further, it is inefficient to inject either too small or too large a volume of gas as compared to the volume of liquid contained within the borehole which does, in fact, need artificial lift. For example, it may be desirable to open a well flow valve and a gas inject valve simultaneously and then close the gas inject valve after a first time period when sufficient pressure is developed in the well to produce continued flow from the well for a second time period. In addition, sequential operation of a pair of motor valves may be desirable such as when two valves are connected to the well output and a first is opened to allow fluid expulsion and then closed while a second valve is simultaneously opened for a time period to allow gas production after the fluid has been cleared. Moreover, it may also be useful to utilize a single controller to sequentially intermit the operation of individual ones of a plurality of wells, each for different selected time periods.
As reservoir engineering technology becomes more sophisticated, more is learned about the various parameters which affect the optimum production of a well, and even the manner in which production from adjacent wells affect each other. It is clear that a system by which a plurality of wells could be controlled for periodic operation to maximize and optimize the production from all wells would be of value. In addition, it would be an advantage to utilize other parameters associated with a producing well, such as casing pressure, tubing pressure, flow rate and pressure and oil/water mix, upon which to base the criteria of when to intermittently open or close a well or when to intermittently inject fluids into the well to stimulate the production of gas and/or liquids therefrom. For example, it would be desirable to open a flowing well when the tubing pressure is greater than an ideal value determined from casing pressure, flowing pressure and gas/liquid ratio.
Moreover, it would be highly desirable to be able to provide a fully programmable controller for the operation of a plurality of motor valves within an array of producing wells whereby various measured parameters from each of the wells could be used to control the intermittent operation of each of those wells in order to optimize the production from all of the wells. The system of the present invention provides such a fully programmable controller for the optimization of well production.
The system of the present invention can be used in multiple applications of producing wells, for example, in gas lift completions, plunger lift completions, wells have fluctuating bottom hole pressures and production flow rate and, in addition, to unload gas wells. In particular, the present invention is especially useful in any type of artificial lift completion which involves the intermittent injection of gas in order to lift liquids to the surface and may also be used to control gas injection into one or more wells in order to optimize the total production of formation fluids from the wells.